An experimental study on the application of Digital Image Correlation (DIC) to measure the deformation and strain of rotating blades is described. Commercial DIC software was used to obtain measurements on three different types of rotors with diameter ranging from 18 to 39 and with varying flexibility to explore applicability of the technique over a breadth of scales. The image acquisition was synchronized with the frequency of rotation such that images could be obtained at the same phase and the consistency of measurements was observed. Bending and twist distributions were extracted from the data with deformation as high as 0.4 measured with a theoretical accuracy of 0.0038 and span-wise resolution of 0.066. The technique was demonstrated to have many advantages including full-field high resolution results, non-intrusive measurement, and good accuracy over a range of scales. The span-wise deformation profiles from the DIC technique are used in conjunction with Blade Element Momentum Theory to calculate the thrust and power consumed by the rotor with rigid vi blades; results are comparable to load cell measurements albeit thrust is somewhat under-predicted and power is over-predicted. Overall, the correlation between DIC calculated thrust and BEMT approximations for comparable blades with constant pitch were within 12% through the onset of stall. Measurement of flexible blade deformation that would not have been possible with other techniques demonstrated the utility of the DIC method and helped to confirm predictions of flexible blade behavior. / text

Three-dimensionally woven composites are a relatively new class of material that offer improved out-of-plane performance by including through-the-thickness mechanical reinforcement compared to traditional laminated composite structures. The mechanical properties are highly dependent upon the weave architecture as this dictates the nature of the through the thickness reinforcement and its effect in improving out-of-plane shear strength. A comparison of two testing methods, Short Beam Strength, and Five Point Bending was conducted over a range of span to thickness ratios with the latter found to be more consistent at producing shear failure over a greater range of span to thickness ratios, although evidence of matrix crushing was present in both, and flexural failure in the Short Beam Strength test. Two weave architectures, the orthogonal and angle weave were subjected to the Five Point Bending test and the failure and damage progression behaviour of both weave architectures were characterised using Digital Image Correlation analysis to measure the edge strain through the thickness of the specimens. This testing showed the angle weave architecture had in general a higher failure strength, and more gradual failure due to longer debonding cracks. The orthogonal weave architecture showed a characteristic post-failure response indicative of crack bridging with discrete load recovery and load drop phases. A numerical model developed from previous work builds on the mosaic modelling method and was modified to include cohesive elements in order to simulate interface debonding via the maximum stress criterion. The simulations are consistently 15 20% greater in failure loads, and 8 - 12% greater in failure shear stresses than those found from the averaged experimental results over the range of tested span to thickness ratios. Post failure response was not modelled. The work presented in this thesis is another step towards gaining a thorough understanding of the mechanical properties of 3D woven composite structures, focussing in particular on out of plane shear strength. The modified mosaic modelling method used showed it is effective at modelling the out of plane testing of orthogonal 3D woven composite structures, and offer the potential to predict the failure of larger composite structures of the same construction and 3D woven architecture although developments are still needed in modelling the post failure response.

La connaissance du comportement de composites sous un état de contraintes multi-axial reste un enjeu majeur pour l’optimisation du dimensionnement des structures. La machine de fatigue bi-axiale présente au LGP permet de générer un état de contrainte bi-axial par l’utilisation d’éprouvettes cruciformes. La conception des éprouvettes reste un enjeu majeur pour les chercheurs pour répondre aux problèmes spécifiques liés aux matériaux composites. Un nouveau type d’éprouvette cruciforme en composite sera conçu en lien avec les problématiques liées au procédé d’infusion de résine liquide (LRI). Il sera ensuite fabriqué avec ce procédé et utilisé pour caractériser le comportement de composites en fatigue bi-axiale. Le suivi des essais sera réalisé en utilisant simultanément un système de corrélation d’images numériques et un système de thermographie infrarouge. La corrélation d’images est une technique optique de mesure de champs qui permet d’obtenir la cartographie des déplacements sur la totalité de la surface de l’éprouvette testée. La thermographie infrarouge permet d’avoir accès à la cartographie de température sur cette surface. Une corrélation entre les données provenant des deux systèmes sera effectuée pour tenter de remonter aux mécanismes d’endommagement des composites lors d’une sollicitation en fatigue bi-axiale. Une corrélation entre des données uni-axiales et bi-axiales sera effectuée. / Knowledge of the behavior of composite materials under multi-axial stress state remains a major objective for structure sizing and optimization. The bi-axial fatigue machine owned by the LGP allows generating a bi-axial stress state, using cruciform specimens. The design of such specimens is a real challenge for researchers to face the specific problems linked to composite materials. A new kind of cruciform specimen will be designed specifically for composite materials manufactured using the liquid resin infusion (LRI) process. It will be manufactured with this process and used to characterize the behavior of composite materials under bi-axial loading. The monitoring of the experiments will be achieved using simultaneously digital image correlation (DIC) to measure the displacements and infrared thermography to measure the temperature variations. DIC is a full field measuring technique which allows obtaining the full cartography of the displacements all over the surface of the specimen. Infrared thermography is also a full field measuring technique used to obtain the cartography of temperature on the whole surface of the specimen. A correlation between the data obtained with both systems will be attempted to identify the damage mechanisms of composites under bi-axial fatigue. A correlation between uni-axial and bi-axial data will also be attempted.

Le projet VERTEX, dans lequel s'inscrivent ces travaux, a pour objectif de valider des modèles composites par essais statiques multi-axiaux sur des éprouvettes à l'échelle des détails structuraux. Le positionnement à cette échelle nécessite de développer de nouveaux outils d'instrumentation et de dialogue essais/calculs, qui sont au cœur de cette thèse. Compte-tenu de la complexité de ce type d'essai, nous nous intéressons ici à la Stéréo Corrélation d'Images Numériques (SCIN) puisqu'elle permet d'accéder à un champ de déplacement 3D à la surface du spécimen. Néanmoins, si l'on s'en tient à des approches classiques, il est difficile de faire une comparaison quantitative entre un champ mesuré et un champ simulé par Éléments Finis (EF). Ainsi dans ce travail, un formalisme est développé pour réaliser une mesure par SCIN dans l'espace physique en se basant sur un modèle EF (calibration de modèles non-linéaires de caméra, mesure de forme EF, mesure de champs EF). Cette méthode donne accès à un champ de déplacement expérimental directement exprimé dans les repère et support EF de la simulation, ce qui simplifie considérablement la validation. Pour valider un modèle à l'échelle des détails structuraux, la question des conditions aux limites est fondamentale. Cette question est d'autant plus complexe que la mesure cinématique se limite à la surface visible. En plus de cette mesure surfacique, il est envisagé ici d'estimer les conditions aux limites dans l'épaisseur en s'appuyant sur un modèle de type plaque/coque (classique ou volumique) et en y accordant plus ou moins de confiance (approches régularisée ou intégrée dans tout ou partie de l'éprouvette). La méthodologie est implémentée dans un logiciel académique et est appliquée sur des essais synthétiques. Une instrumentation adaptée au banc VERTEX a également permis l'analyse des essais réalisés dans le projet. / VERTEX Project, to which this thesis belongs, aims to validate composite models by multi-axial static tests on specimens at the level of structural details. The positioning on this scale requires the development of both new instrumentation techniques and tools for the test/simulation dialogue, which are at the heart of this thesis. Given the complexity of this type of experiments, we focus here on Stereo Digital Image Correlation (SDIC) since it yields 3D displacement fields on the surface of the specimen. However, if we stick to conventional approaches, it is difficult to make quantitative comparisons between a measured field and a Finite Element (FE) simulated field. Thus, in this work, a framework is developed to make a measurement by SDIC in the physical coordinate system based on an FE model (calibration of non-linear camera models , FE shape measurement, FE field measurement). This method gives access to experimental displacement fields directly expressed both in the coordinate system and support of the FE simulation, which considerably simplifies validation. To validate a model at the scale of structural details, the question of boundary conditions is fundamental. This question is even more complex since the kinematic measurement is limited to the visible surface. In addition to this surface measurement, it is here envisioned to estimate additionally the boundary conditions in the thickness of the specimen relying on a plate/shell-like model (classic or volume). Different approaches are considered depending on the confidence giving to this model. This methodology is implemented in an academic software and is applied to synthetic tests. The development of a dedicated instrumentation also allowed the analysis of tests performed on the VERTEX bench.

abstract: The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in Arizona State University by Dr. Barzin Mobasher and Dr. Chote Soranakom. Intrinsic material property of moment-curvature response for SHCC was used to derive the relationship between applied load and deflection in a two-step process involving the limit state analysis and kinematically admissible displacements. For application of SHCC in structures such as shear walls, tensile and shear properties are necessary for design. Lot of research has already been done to study the tensile properties and therefore shear property study was undertaken to prepare a design guide. Shear response of textile reinforced concrete was investigated based on picture frame shear test method. The effects of orientation, volume of cement paste per layer, planar cross-section and volume fraction of textiles were investigated. Pultrusion was used for the production of textile reinforced concrete. It is an automated set-up with low equipment cost which provides uniform production and smooth final surface of the TRC. A 3-D optical non-contacting deformation measurement technique of digital image correlation (DIC) was used to conduct the image analysis on the shear samples by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-field strain distribution, displacement and strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and gave a relation between shear angle and shear strain. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2014

Com os crescentes movimentos ecolÃgicos em todo o mundo, onde o objetivo principal visa conscientizar e estimular a populaÃÃo mundial a poupar os recursos naturais, aliado a necessidade de se desviar os resÃduos aterrados (sanitÃrios ou industriais), de forma a reduzir os problemas ambientais e de saÃde pÃblica, decorrentes da disposiÃÃo inadequada de resÃduos sÃlidos, surgem os incentivos a reciclagem de materiais, bem como o desenvolvimento de materiais biodegradÃveis. Diante deste contexto, os materiais compÃsitos reforÃados com fibras naturais ganham destaque no meio cientÃfico. No entanto, seu uso ainda à tido com desconfianÃa, devido ao pouco ou nenhum conhecimento desses promissores materiais. Perante essa problemÃtica, surgiu a proposta deste trabalho de carÃter investigativo, em que foi pesquisado e desenvolvido um compÃsito totalmente reciclado, de matriz termoplÃstica (PVC reciclado) reforÃado, com fibras obtidas da casca de cocos verdes descartados. Para esse objetivo foram utilizadas diversas ferramentas de caracterizaÃÃo fÃsica, quÃmica, tÃrmica e mecÃnica, sendo os valores dos campos de deformaÃÃo obtidos pela CorrelaÃÃo de Imagem Digital (CID), comparando a imagem do corpo nÃo deformado com imagens do corpo deformado. E finalmente, avaliou-se os processos de danificaÃÃo do compÃsito, atravÃs da caracterizaÃÃo experimental da evoluÃÃo do dano isotrÃpico pelos mÃtodosda variaÃÃo do MÃdulo de Elasticidade efetivo (ensaio de traÃÃo com carga e descarga) e pelo Ãndice de Tsai-Wu com os parÃmetros constitutivos da funÃÃo tangente hiperbÃlica, onde os valores encontrados, em ambos os mÃtodos, mantiveram-se dentro da faixa esperada para compÃsitos, 0,20 â 0,50. / With increasing the ecological movements around the world, whose the main objective aims to raise awareness and encourage the world's population to save natural resources, coupled with the need to divert grounded waste (sanitary or industrial) in order to reduce environmental problems and public health, arising f rom the improper disposal of solid waste, emerge incentives for recy cling, and the development of biodegradable materials. Given this context, the composites reinforced with natural fibers began to be highlighted in the scientific community. However, its utilization is still seen with suspicion due to little or no knowledge of these pr omising materials. Faced with this problem, arose the proposal of this investigative character work, in with it was researched and devel oped a fully recycled composite, of thermoplastic matrix (recycl ed PVC) reinforced with fibers obtained from the bark of green coconut s discarded. For this objective were used various tools of physical, chemical, thermal and mechanical characterization, whose amounts of d eformation fields were obtained by Digital Image Correlation (DIC), c omparing the image of the body not deformed with images of the deforme d body. Finally, we assessed the processes of damage of the composite, through experimental characterization of the evolution of t he isotropic damage by the methods of varying the effective elastic mod ulus (tensile test with loading and unloading) and by Tsai-Wu index wi th the parameters constitutive of hyperbolic tangent function, where the values found, in both methods, were within the expected range for composite, from 0.20 to 0.50.

L'identification du comportement des polymères et notamment des élastomères reste un problème délicat. Dans ce travail, nous proposons une méthode d'identification qui associe la mesure de champ de déformation par analyse d'images avec l'optimisation d'un champ de contraintes adapté à l'essai. L'essai retenu est un étirage biaxial réalisé sur une éprouvette en forme de croix. L'approche proposée transforme l'inconvénient de l'hétérogénéité en avantage puisqu'il permet de réaliser l'identification simultanée sur plusieurs états de déformation : typiquement traction uniaxiale, plane et biaxiale. Le champ de contrainte est approché par la somme d'un champ homogène et d'un champ complémentaire vérifiant les conditions de bords libres et qui décroît lorsqu'on pénètre dans l'échantillon. La longueur caractéristique de la décroissance est optimisée de telle sorte que le champ approché vérifie au mieux les équations d'équilibre. En combinant l'analyse d'images avec le champ de contrainte optimisé, on identifie le potentiel hyperélastique en calculant explicitement les deux dérivées f=∂W/∂I1 et g=∂W/∂I2 où et sont les deux 1er invariants du tenseur de Cauchy droit. Enfin, un algorithme spécifique est mis en oeuvre par éléments finis pour une simulation 2D des matériaux hyperélastiques incompressibles. Cet algorithme est utilisé pour valider l'identification en comparant les résultats de la simulation et ceux de l'expérience / The identification of the polymer's behaviour and especially rubber-like materials remains a challenging task. In this work, we propose a method for the identification which combines strain field obtained by digital image analysis and the optimisation of an approximated stress field adapted to the specimen geometry. A biaxial stretching test is performed on a crosshair rubber specimen. With the proposed approach, heterogeneity of the strain field during this equi-biaxial tension test becomes an advantage. It allows the simultaneous identification of several strain states: uniaxial, biaxial and planar elongations as well as shear. The stress field is approximated by the sum of a homogeneous field and an additional field. The latter, checking the boundary conditions on the free edge is decreasing when entering the sample. The characteristic decreasing length is optimized so that the approximate field verifies the equilibrium equations. Combining image analysis with an optimized stress field, we manage the identification the hyperelastic potential by calculating explicitly the two derivatives f=∂W/∂I1 and g=∂W/∂I2 and conclude on their dependence on I1 and I2 the two first invariants of the rigth Cauchy-Green tensor. Finally, a specific finite element algorithm has been developed to similate a 2D-incompresible hyperelastic material. This algorithm is used to validation the identification potentiel by comparing simulation results and experimental data

Aluminium sheet production is a multi-stage process in which altering processing conditions can drastically alter the size and type of second phase particles found in the final product. The properties of these second phase particles also affects deformation and annealing processes, meaning that any attempt to create a through process model would require the ability to predict both how the particles would develop in the material, and how these particles then affect the alloy moving forward. This project first focuses on gaining insight into how the particles in a model aluminium alloy change during homogenisation heat treatment and hot rolling. This has been accomplished by utilising serial block face scanning electron microscopy (SBF-SEM), a technique which allows the capture of 3D data sets at sub micron resolutions. This has allowed the populations of primary (constituent) and secondary (dispersoid) particles to be analysed at different stages of sheet production, and thus allowing the effects of homogenisation and hot rolling on particle populations to be quantified. To discover how the particles would go on to affect further processing, digital image correlation has been used to examine the localised strain in the alloy near to a selection of particle configurations. This highlighted the heterogeneity in slip behaviour within the alloy and illustrated that plumes of rotation develop near to non deformable regions. Rotation plumes have previously been modelled using a crystal plasticity model, and so further work is also presented expanding upon this model to simulate a variety of particle configurations. This has shown that in the case of single particles, local deformation is dependent on both the aspect ratio of the particle and how it is aligned to the active slip system. With the incorporation of a second particle, the interparticle spacing must also be considered.

Les matériaux composites 3D obtenus par couture ou piquage transverses présentent de nombreux atouts comparativement aux tissages interlocks ou orthogonaux 3D. Dans le but d’évaluer le potentiel de cette nouvelle génération de matériaux 3D, certaines études ont été consacrées à leur caractérisation mécanique. D’autres études se sont focalisées sur l’influence de certains types de coutures sur la perméabilité de matériaux cousus de type NCF (Non Crimp Fabrics). Cette thèse se propose d’étudier l’apport des coutures de type Tufting dans le renforcement transverse de tissus classiques 2D. Cet apport est évalué, conjointement, du point de vue mécanique et du point de vue de la perméabilité. Parmi les nombreux paramètres de couture, l’étude s’est focalisée sur l’influence de la densité de couture. A ce titre, trois différentes densités de coutures ont été réalisées, grâce à un robot de couture disponible au sein de notre laboratoire. Du point de vue de la perméabilité, les préformes cousues ont été réalisées avec des empilements identiques à ceux des préformes non cousues. L’évaluation des perméabilités a été conduite à travers un banc de mesure de perméabilité à flux unidirectionnel. Avec cette méthode, le tenseur de perméabilité plane est obtenu à travers trois mesures unidirectionnelles : 0° (chaine), 90° (trame) et 45°. L’analyse des résultats montre que la couture de type Tufting induit un effet atténuateur du rapport d’anisotropie K1/K2. D’autre part, il ressort que la position du fil de couture provoque des gradients de perméabilités locaux, très prononcés entre la surface et le cœur de la préforme. Pour les besoins de la caractérisation mécanique, six plaques composites ont été réalisées par le procédé RTM. Pour atteindre les caractéristiques mécaniques hors-plan, des plaques de 20 mm d’épaisseur, cousues et non cousues ont été réalisées. La CIN (Corrélation d’Image Numérique) a été utilisée pour cartographier les distributions des champs de déplacement lors des essais mécaniques (traction, compression sur cube et flexion en poutre courte), ceci afin de tenir compte de la présence des coutures au sein des matériaux. Les performances mécaniques évaluées se sont révélées bien en deçà des attentes, surtout en ce qui concerne les caractéristiques hors-plan. L’analyse micrographique des matériaux a révélé la présence de porosités concentrées au sein, ou dans le voisinage proche, des coutures. D’autre part, les coutures présentaient des courbures ou vrillages, provoquées par le compactage lors de la fermeture du moule RTM.En faisant le lien avec les résultats de perméabilité, il ressort que la présence des porosités au sein des coutures est une conséquence des gradients de perméabilité qui induisent des refermetures de flux d’imprégnation. / 3D composite materials, which obtained by stitching or tufting, have many advantages compared to the 3D orthogonal weaves or interlocks. ln order to evaluate the potential of this new generation of 3D materials, some studies have been devoted to their mechanical properties. Other studies have focused on the influence of certain types of seams on the permeability of materials such as NCF (Non Crimp Fabrics).This thesis is to study the contribution of seams through the thickness of reinforcement 2D classic fabrics. This contribution is evaluated the mechanical properties and their permeability at the same time. Among many stitching parameters, the study focused on the influence of the stitching density. Three different seams densities were carried out through a robot available in our laboratory.ln terms of permeability, the stitched preforms were laminated those of identical unstitched preforms by using Tufting.The evaluation of permeability was conducted in an unsaturated regime through a small scale bench test by the unidirectional flow. With this method, the in-plane permeability tensor is obtained through the measured permeability in three directions : 0° (warp), 90° (weft) and 45°. The results show that the type of Tufting seams reduces the effect of anisotropy ratio Kl/K2. And it is obvious that the position of the stitching thread causes local permeability gradients very pronouncedly between the heart and the surface of the preform. For the purposes of the mechanical properties, six composite plates were made by the RTM process. To achieve mechanical properties through the thickness of the plates of 20 mm thick, stitched and unstitched performed were prepared. DIC (Digital Image Correlation) was used to detect the distribution of displacement fields during mechanical testing (tensile, compression and short bearn bending) in order to take account of the presence of seams within materials. The measured mechanical performance proved below expectations, particularly with regard to the characteristics in the third direction. Micrographie analysis of materials revealed the presence of porosity concentrated within, or near the seams. Moreover, the bends or kinks of seams were caused by compaction during closure of the RTM mold. By connecting with the permeability data, it appears that the presence of porosities in the seams is a consequence ofpermeability gradients that induce impregnation flow reclosing.

This thesis presents work on investigations into the mechanical properties of connective tissue. A model system of hydrogels was used to investigate how volume change through water flow is coupled to relaxation. This was done using digital image correlation (DIC) and a custom built setup. It was found, in hydrogels, that water loss is directly coupled to an increase in tension and water intake is directly coupled to tension relaxation. The experimental setup was tested by investigating the mechanical properties of the well known material polydimethylsiloxane (PDMS) and the novel materials of carbon nanotube (CNT) elastomers, cholesteric liquid crystal elastomers (CLCEs), and 3D polydomain liquid crystal elastomers (3DLCEs). The setup accurately demonstrated the incompressibility of PDMS, even at short time scales, and demonstrated how DIC can map the inhomogeneity of material by locating clusters of CNTs in CNT elastomers by how they deform. Novel results for 3DLCEs were also found, where it was discovered that there is a softening of the bulk modulus at small time scales resulting in a volume increase following deformation, the bulk modulus then recovers and there is over all no volume change. This is in stark contrast to the typical case, where it is the shear modulus that becomes comparable to the bulk modulus, resulting in increased volume. A theoretical investigation was carried out into critical damping in viscoelastic oscillators, where the aim was to apply to the findings to connective tissue. The fractional Maxwell model and zener model where both solved for, where it was found that damping decreases as the material becomes more solid and the peak of critical damping becomes broader. Finally, investigations into how strain relates to the viscoelastic properties of connective tissue were carried out on horse tendon and rat fascia. How relaxation changes was determined through the relaxation constant, where a large constant means it takes the sample longer to relax and it is more solid like. It was found, that in general, the relaxation constant increases quickly with an imposed strain and then either stabilises or increases more slowly. This growth of relaxation constant also occurs during the initial stages of tissue injury, where irreversible deformation occurs.